1. Field of the Invention
The present invention relates to a screen printing apparatus and a screen printing method which print a pattern with paste on the surface of a substrate which is aligned with a mask in which predetermined pattern openings are formed.
2. Related Art
In a mounting process of electronic components, screen printing of supplying a pasted conductive material (conductive paste, hereinafter simply referred to as ‘paste’) onto the surface of a substrate is used frequently in order to mechanically and electrically join electronic components to the substrate. The screen printing includes supplying paste onto the surface of a mask provided with pattern openings formed in a predetermined pattern in a state where the mask is brought into surface contact with the surface of a substrate, and applying and spreading the paste on the surface of the mask by means of a squeegee which slides on the surface of the mask, thereby printing a pattern on the surface of the substrate with the paste stagnated in the pattern openings. Electronic components are placed on the part where a pattern is printed with the paste, and the electronic components are mounted on the substrate in a state where they are mechanically and electrically joined together with the paste cured through a reflow process.
In the screen printing, it is important to accurately print a paste at a predetermined position of the substrate surface and it is necessary to align the substrate with the mask in high precision. In the position alignment, the position misalignment is set as the displacement of the substrate to perform the position alignment compensation by photographing the positions of recognized parts respectively formed on the substrate and the mask with the recognition device including a camera, etc. (for example, refer to JP-A-2001-38876 and JP-A-11-245369).
In a screen printing apparatus disclosed in JP-A-2001-38876, respective recognized parts are photographed with one camera provided on both substrate and mask. By this configuration, when the recognized part of the substrate disposed on a lower side of the mask is photographed, it is necessary to draw out the substrate from the lower side of the mask. Therefore, it is necessary to secure a space for drawing out the mask, thereby causing the apparatus to be enlarged.
Meanwhile, in the screen printing apparatus disclosed in JP-A-11-245369, the recognition device including two cameras such as a camera photographing the recognized part formed on the surface of the substrate and a camera photographing the recognized part formed on the rear face of the mask is disposed between the substrate and the mask. By this configuration, it is possible to photograph the recognized part without drawing out the substrate, but it is necessary to increase the clearance between the substrate and the mask at the time of the position alignment since two cameras are vertically stacked to arrange the optical axes of the respective cameras on a same plumb line. As the result, the stroke raised to contact the substrate to the mask after the position alignment compensation becomes longer, whereby the position alignment accuracy of the substrate and the mask is reduced.